A. Field of the Invention
The present invention relates to an improvement in a cage type wire twisting machine for twisting wire-like structures which have weak tensile strength, such as communication wires, optical fiber core wires, or the like, into a cable.
B. Description of the Prior Art
In common practice, a plurality of communication wires, optical fiber core wires, or the like, are twisted into a cable, and a plurality of such individual cables are in turn gathered into a larger cable. Among the several kinds of twisting machines used for this purpose, a cage type twisting machine is one of the most widely used. With this machine, it is possible to perform twisting while effecting twisting-back. This prevents internal distortion from occurring due to the twisting of the wire-like structures and also prevents the twisted wire-like structures from untwisting at the end, when cut. Twisting-back is particularly important in the case of optical fiber core wires because internal distortion may deteriorate significantly optical performance. Further, in the case of wire-like structures having weak tensile strength, it is necessary to maintain the tension of the wire-like substance in the wire-twisting machine at a constant low level. To achieve this end, feeding speed of the wire structure supply bobbin is controlled by a variable speed motor, as is conventionally known.
In a conventional cage type wire twisting machine, as shown in FIGS. 1, 1a and 2, a spindle 1 is rotatably supported by bearings 2 and 3 provided on a stand for the machine. Disks 4 and 5 are fixed on the spindle 1 which is rotated by a driving electric motor 62. A cradle 6 is rotatably supported by bearings 8 and 9 respectively provided between the disks 4 and 5. Bobbin 7 on which a wire-like structure is wound is rotatably held by the cradle 6. A plurality of cradles 6 corresponding to the number of the wire-like structures to be twisted are disposed circumferentially around and coaxially with the spindle 1 as shown in FIG. 2, and the cradles are arranged such that they revolve with the disks 4 and 5 around the spindle 1. Each cradle does not turn on its own axis as the spindle 1 rotates, so as to maintain a constant plane and thereby to prevent the wire-like substance from twisting. This is referred to as a "twisting-back operation". As shown in FIGS. 1 and 1a, guide rollers 10 and 11 are provided in the cradle 6. Guide roller 10 has a fixed shaft while guide roller 11 is arranged to be slidable in the direction of arrow 70 along guide rails 13. The wire-like structure 20 is fed from the bobbin 7 and further fed through the guide rollers 10 and 11. In this case, the position of the guide roller 11 is detected by position detector (not shown in the Drawing). A detection signal is fed back to a controller 16 provided in the cradle 6 to control the rotation of the bobbin 7 driven by a bobbin driving motor 12 through a belt 12' to control the wire-like structure feeding speed so as to put the guide roller 11 always at a substantially fixed position. Accordingly, the wire-like structure 20 is fed out of the bobbin 7 with substantially zero tension. The controller 16 and the motor 12 are energized from an external power source through slip rings 14 and 15. A tension application device (not shown in the Drawing) is incorporated into the guide roller 11 to maintain constant the tension of the wire-like structure 20. The wire-like structure 20 advances from the guide roller 11 to an axis hole of the cradle 6 and a guide roller 17 attached to the disk 4 through strap 18 of spindle 1 and finally through a twisting die 19 into twisted cable 72. In this apparatus, the wire-like structure 20 is fed out of the bobbin 7 with substantially zero tension due to the function of the controller 16 and the variable speed driving motor 12 in accordance with the position of the guide roller 11. The tension acting on the wire-like structure when it is twisted is only that applied by the tension application device of the guide roller 11 so that the twisting operation can be performed with a constant low tension. Further, as shown in the Drawing, a hole may be formed through the spindle at its center and a core wire 73 may be passed through the hole so that the wire-like structures 20 may be twisted around the core wire. Further, a brake 74 is provided on the spindle 1 for additional control of the wire-like structure twisting machine.
In the conventional twisting machine as described above, with reference to the Drawing, electric devices, such as the controller 16, the driving motor 12, or the like, are individually incorporated into each cradle 6 which revolves. This increases the size of the cradle-disk assembly and results in a large diameter of revolution. Accordingly, much vibration and a large centrifugal force are always present at the controller when the cradle is revolving. Consequently, such wire twisting machines have operational disadvantages especially with respect to the mechanical parts, particularly such as relays, switches, or the like, resulting in malfunctions and a tendency for occurrence of faults. Further, there is a disadvantage that since the controller and the motor are individually disposed in the respective cradle, the cradle is large in mass, size and its diameter of revolution so as to be more affected by the centrifugal force. Further, since the controller and motor are individually disposed in each respective cradle, the entire construction is complicated and maintenance is difficult.